Import of nuclear DNA-encoded RNAs into mitochondria and mitochondrial translation

Targeting nuclear DNA-encoded tRNA into mitochondria is a quasi-ubiquitous process, found in a variety of species, although the mechanisms of this pathway seem to differ from one system to another. In all cases reported, this import concerns small non-coding RNAs and the vast majority of imported RNAs are transfer RNAs. If was commonly assumed that the main criterion to presume a tRNA to be imported is the absence of the corresponding gene in mitochondrial genome, in some cases the imported species seemed redundant in the organelle. By studying one of such "abnormal" situation in yeast S. cerevisiae, we discovered an original mechanism of conditional regulation of mitochondrial translation exploiting the RNA import pathway. Here, we provide an outline of the current state of RNA import in yeast and discuss the possible impact of the newly described mechanism of translational adaptation.